kicker idea input

[Eric Schneider]

M(kicker) * V(kicker) = M(ball) * V(ball)

This is true, but the problem is if you are accelerating the kicker, F=ma and if the force being applied by the surgical tubing or spring or whatever stays constant and the weight goes up, it will decrease the acceleration. It's a take some, lose some sort of thing. If you drop your kicker and it is accelerated by gravity, more weight is better.

On the other hand, the longer you give the leg to accelerate (longer swing) the greater the velocity of the kicker. We're thinking of ways to either give the kicker as long a leg as possible or pull it back farther to give it more swing time. This decreases the forces we are playing with a bit and makes it safer, for one. When playing with these coiled or stored forces capable of kicking a ball across the field I'm kinda scared somebody's going to get smacked in the building process. Safety safety safety

[RRLedford]

Originally Posted by Eric Schneider

M(kicker) * V(kicker) = M(ball) * V(ball)

This is true, but the problem is if you are accelerating the kicker, F=ma and if the force being applied by the surgical tubing or spring or whatever stays constant and the weight goes up, it will decrease the acceleration. It's a take some, lose some sort of thing. If you drop your kicker and it is accelerated by gravity, more weight is better.

On the other hand, the longer you give the leg to accelerate (longer swing) the greater the velocity of the kicker. We're thinking of ways to either give the kicker as long a leg as possible or pull it back farther to give it more swing time. This decreases the forces we are playing with a bit and makes it safer, for one. When playing with these coiled or stored forces capable of kicking a ball across the field I'm kinda scared somebody's going to get smacked in the building process. Safety safety safety

You can look at ways to keep the force at max during the full travel of the kicker's travel. With pneumatics, have a longer cylinder with most of its volume pressurized behind piston at START of kick and also use less travel of piston (more leverage & short stroke).
With bungees, preload tension in them so decent force is still being applied to kicker at end of its travel as well as at start, instead of force being zero at end of travel. Basically do what can be done to maintain full force for the full travel of the kicker.
-RRLedford

[AndrewJS]

M(kicker) * V(kicker) = M(ball) * V(ball)

That is close but not quite correct. Momentum is conserved, and energy is conserved.

Therefore:

Conservation of Momentum
M(kicker)*V(kicker[before]) = M(Ball)*V(Ball) + M(Kicker)*V'(kicker)

Where V(kicker[after]) is the speed of the kicker after hitting the ball (do not assume this is 0).

Conservation of Energy
KE(kicker[before]) = KE(ball) + KE(Kicker[after]) + Eint

(Where KE = 1/2mv^2 and Where Eint is the internal energy lost to deformation of the ball, I suppose you could include others like heat as well, but I don't see too much heat being created here). I ran an experiment in my garage (bouncing a soccer ball on my cement floor, recording with a camera, and analyzing the height of each bounce) and saw that roughly 60% of the kinetic energy of the soccer ball was lost on each bounce. I have not run equations taking this loss into effect, but my guess is that Eint = .4*KE )

Collisions can be elastic, inelastic or somewhere in between. Elastic means that kinetic energy is completely conserved (Eint in this case would be 0). Inelastic means kinetic energy is not conserved.

For sake of equations, lets assume the collision between a kicker and a soccer ball is completely elastic, so Eint = 0. You can then solve the two above conservation equations (took me a full page) but you get in the end:

V(ball) = 2 * V(kicker) * M(kicker) / ( M(ball) + M(kicker) )

Lets take the case where M(kicker) is much greater than the mass of the ball. Taking a limit as M(kicker) -> inf, Then:
V(ball) = 2 * V(kicker)

This is the maximum velocity you can ever hope to achieve with the ball (twice that of the kicker). As Walter Lewin (MIT) would say, "very non-intuitive." Nevertheless, don't concentrate on making your kicker too massive. The real key is balancing having enough mass and speed, as mentioned before using F = ma where your kicking force will be constant (if you are using a spring/elastics and pull it back to the same spot each time).

Yet this doesn't take into account the loss of energy due to Eint. You'd have to re-solve all the equations for this. Or, just plan on designing something about twice as powerful as it is in theory.

This is the point where I stopped doing equations (trying to calculate everything was getting quite ridiculous) and just built a kicker prototype, which actually worked quite well at throwing balls across the room and breaking ceiling tiles. We are going with a spring loaded pullback (our prototype used bungee cords) Still working out details for a fast and strong winch to pull it back. Our wish is to have the release be adjustable, this will give use the advantage of selecting how hard we want to hit it. If all else fails, we can use a (probably simpler) system to release it at the same spot every time.

[RRLedford]

Team 3135 failed miserably with its RAM kicker accelerated by bungies!

Our PVC pipe ram kicker prototype, with 1-1/4" pipe sliding inside 2" pipe was kicked powerfully ONLY when hitting ball dead center, but could not elevate at that contact spot. The end of pipe had a tee in it to hit ball like a hammerhead shark, but even with good speed, hitting much below center killed all the power delivered. It seemed that too much torque and bending was happening as the 1-1/4 pipe extended much beyond the 2" guide pipe. There was no ram wiggle at all, and it was almost frictionless sliding, but this scheme would not elevate at all. This is the nature of compression - it wants to buckle and bend things out of alignment and initiate torque, whereas tension pulls things into alignment with each other.

So we went back to doing a bungee driven two arm pendulum, building a final scheme with metal parts today, and using ball bearing 5/8 swing axle. Already, we are up to 40 feet airborne without even very much optimization. The pendulum kicker produces elevation of kicks SO much more easily than the ram, and it is far simpler to tune for proper ball contact.

We are still intending to use a CIM+gearbox as a winder for bungee pulling to store energy. The winder sits between kicker and bungees, which all have one of their ends anchored on the frame. Cable passes through winder which can shorten cable by from 0-20" with a 0-180 degree cable wind. Cable can be instantly disengaged from winder - AT ANY # DEGREES INTO THE WIND UP CYCLE - allowing snap back to a straight un-wound state, and variable energy release under programmable controll based on how far the winder is rotated before cable is released. This way we have variable kick energy at programmed levels.

Pneumatics can do too, this using a programmed valve open interval to limit level of pressure build up for shorter kicks.

Our design for the winder's pneumatic trigger mechanism for disengaging cable from winder is being tested using wood on Sat. If all goes well, we will be cutting metal to finish kicker bu Thr. Will post results as we progress.
-RRLEDFORD

[Ether]

Originally Posted by RRLedford

Team 3135 failed miserably with its RAM kicker accelerated by bungies!

Our PVC pipe ram kicker prototype, with 1-1/4" pipe sliding inside 2" pipe was kicked powerfully ONLY when hitting ball dead center, but could not elevate at that contact spot. The end of pipe had a tee in it to hit ball like a hammerhead shark, but even with good speed, hitting much below center killed all the power delivered.

Get rid of the hammerhead tee and replace it with a sloped surface (like a cattle guard on the front of a train). Then you will get lots of lift.


.

[mrcolling]

Originally Posted by AndrewJS

That is close but not quite correct. Momentum is conserved, and energy is conserved.

Therefore:

Conservation of Momentum
M(kicker)*V(kicker[before]) = M(Ball)*V(Ball) + M(Kicker)*V'(kicker)

Where V(kicker[after]) is the speed of the kicker after hitting the ball (do not assume this is 0).

Conservation of Energy
KE(kicker[before]) = KE(ball) + KE(Kicker[after]) + Eint

(Where KE = 1/2mv^2 and Where Eint is the internal energy lost to deformation of the ball, I suppose you could include others like heat as well, but I don't see too much heat being created here). I ran an experiment in my garage (bouncing a soccer ball on my cement floor, recording with a camera, and analyzing the height of each bounce) and saw that roughly 60% of the kinetic energy of the soccer ball was lost on each bounce. I have not run equations taking this loss into effect, but my guess is that Eint = .4*KE )

Collisions can be elastic, inelastic or somewhere in between. Elastic means that kinetic energy is completely conserved (Eint in this case would be 0). Inelastic means kinetic energy is not conserved.

For sake of equations, lets assume the collision between a kicker and a soccer ball is completely elastic, so Eint = 0. You can then solve the two above conservation equations (took me a full page) but you get in the end:

V(ball) = 2 * V(kicker) * M(kicker) / ( M(ball) + M(kicker) )

Lets take the case where M(kicker) is much greater than the mass of the ball. Taking a limit as M(kicker) -> inf, Then:
V(ball) = 2 * V(kicker)

This is the maximum velocity you can ever hope to achieve with the ball (twice that of the kicker). As Walter Lewin (MIT) would say, "very non-intuitive." Nevertheless, don't concentrate on making your kicker too massive. The real key is balancing having enough mass and speed, as mentioned before using F = ma where your kicking force will be constant (if you are using a spring/elastics and pull it back to the same spot each time).

Yet this doesn't take into account the loss of energy due to Eint. You'd have to re-solve all the equations for this. Or, just plan on designing something about twice as powerful as it is in theory.

This is the point where I stopped doing equations (trying to calculate everything was getting quite ridiculous) and just built a kicker prototype, which actually worked quite well at throwing balls across the room and breaking ceiling tiles. We are going with a spring loaded pullback (our prototype used bungee cords) Still working out details for a fast and strong winch to pull it back. Our wish is to have the release be adjustable, this will give use the advantage of selecting how hard we want to hit it. If all else fails, we can use a (probably simpler) system to release it at the same spot every time.

Greetings

The ball when compressed is like a spring and stores some energy which is then released as the ball regains its shape. When a human kicks a ball the follow through past the point of impact is important. The mass at the end of the kicker should stay moving in the direction of the target during this compression of the ball otherwise energy will just be sent back to the robot. I would think some forward motion of the robot combimed with the kick would give positive results for maximum force.

[riptide]

I tried to post this before but since I am new to the site I don't think it allowed me to make a post with a link.

RoboCup has been around for a long time now and they have really perfected the kicking mechanism. Here is a link to a white paper that may help you out. Keep in mind the solenoid is illegal.


http://roboturk.googlecode.com/files..._mechanism.pdf

[riptide]

I tried to post this before but since I am new to the site I don't think it allowed me to make a post with a link.

RoboCup has been around for a long time now and they have really perfected the kicking mechanism. Here is a link to a white paper that may help you out. Keep in mind the solenoid is illegal.


roboturk.googlecode.com/files/robocup_shooting_mechanism.pdf

[tomgee4me]

Has anyone considered the bumper overhang? I'm having a tough time with all the bumper restrictions severely limiting design choices. 10" high over a 9" diameter ball. If the ball rolls further than 4.5" under the bumper, a 45 degree kick will not clear it!

[thefro526]

Originally Posted by tomgee4me

Has anyone considered the bumper overhang? I'm having a tough time with all the bumper restrictions severely limiting design choices. 10" high over a 9" diameter ball. If the ball rolls further than 4.5" under the bumper, a 45 degree kick will not clear it!

Raise your bumpers up to the maximum height of the bumper zone which is 16". This should position the bottom of your bumpers at about 10.75" - 11" from the floor. (assuming bumper height of ~5")

This should free up a bit more room for your kicker.